1. Field of the Invention
This invention relates to the method of hollow-spindle machine tools, and particularly lathes, for primary and secondary machining, successively, a number of short-length workpieces.
The term "short-length workpieces" as hereinused means a workpiece which is holdable by a chuck. Thus, elongated bars, rods and the like are excluded.
2. Description of the Prior Art
It is frequently necessary in the field of machining to execute a primary and a secondary machining successively on opposite ends, respectively, of each of a large number of similar workpieces with a single machine tool.
A representative conventional method for this uses two rotatable spindles carrying chuck units arranged in opposition to each other, at least one of these spindles reciprocating along the common axis of the two. In this case, the primary machining is carried out while the workpiece is held by one chuck unit, and then the secondary machining is executed upon transfer of the workpiece to the second chuck unit. For this, reference may be had to U.S. Pat. No. 4,457,193.
It is also known to use one spindle carrying a single chuck unit. In this case, the primary machining is carried out while the workpiece is held by the single chuck unit, and then either a robot or a loader provided with a position reverser is used. The already primary-machined workpiece is released from the chuck unit, subjected to the position-reversing operation of the robot or loader and rechucked in the same chuck unit.
In the former case, with the two spindles, at least one of the spindles must be mounted on a reciprocable feeder, thereby requiring increased space and manufacturing cost for the machine tool.
In the latter case, the robot or loader must be additionally provided, again requiring increased space and cost.